The present invention relates to methods for the formation of silicon oxide films on the surfaces of substrates. More specifically, the present invention relates to methods for the formation of thick ceramic silicon oxide films that are free of cracks and pinholes and that are insoluble in organic solvents.
The formation of protective films on the surface of substrates is a technique in general use. In the particular case of the electric/electronic industries, recent increases in the degree of integration and layer count of semiconductor devices has resulted in a very substantial increase in their complexity and in topographical variations on their surface. In the case of multi-layer circuits, an interlevel dielectric layer may be formed on the surface of semiconductor devices for purposes of planarization and insulation between interconnections. Alternatively, a passivation coating may be laid down on the surface of a semiconductor device in order to planarize the topographical variations on the semiconductor device surface and protect it from mechanical damage, chemical damage, damage due to static, ionic contaminants, nonionic contaminants, radiation damage, and so forth.
Silicon oxide films are typically used for these interlevel dielectric layers and passivation coatings. Chemical-vapor deposition (CVD) and spin-coatings are examples of the methods used to form these silicon oxide films. Spin-coating methods are exemplified by the use of inorganic SOG (spin-on glass) and organic SOG.
However, the silicon oxide films formed from inorganic SOG suffer from cracking at film thicknesses in excess of 0.3 micrometers. This has made it necessary to carry out multiple applications in order to level height differences of 1 micrometer or more. Moreover, a particular problem with this technology is that the film itself has a poor capacity to bring about planarization, thus requiring an etch-back planarization step after film formation.
By contrast, the silicon oxide films formed from organic SOG are capable of forming crack-free films in thicknesses of 1 micrometer and more by a single application. However, as with inorganic SOG, the organic SOG film itself has a poor planarization capability, and this has also necessitated the execution of an etch-back planarization step after film formation. In addition, the silicon oxide films obtained from organic SOG contain large quantities of residual silanol and alkoxy groups and are therefore highly hygroscopic. Moreover, due to the residual alkoxy groups these films suffer from the problem of carbon poisoning (carbon contamination) in the case of oxygen plasma treatment. As a result of these characteristics, these films have a poor electrical reliability when used for the formation of an interlevel dielectric.
The use of hydrogen silsesquioxane to form silicon oxide films has been proposed (Japanese Patent Application Laid Open [Kokai or Unexamined]Number Hei 3-183675 [183,675/1991]) in order to improve upon the above-described problems. Because this resin melts when heated, it exhibits an excellent capacity to planarize topographical variations and, therefore, does not require an etch-back process. Moreover, since organic groups are not present among this resin's structural units, the risk of carbon poisoning during oxygen plasma treatment is avoided.
The silicon oxide film-formation method proposed in Japanese Patent Application Laid Open Number Hei 3-183675 cannot, however, produce silicon oxide films more than 0.8 micrometers (8,000 angstroms) thick. As a result, this method cannot completely planarize the topographical variations encountered on the surfaces of semiconductor devices, i.e., topographical variations on the surface of a semiconductor device in excess of 0.8 micrometers (8,000 angstroms). In addition, when the production of a thick silicon oxide film is attempted by this method, cracks and pinholes are produced, thus reducing the reliability of the semiconductor device.
Finally, it has been difficult to form well-shaped contact holes in the above silicon oxide films using haloalkane plasma etching because of the large difference in etch rates between the aforesaid silicon oxide films and plasma CVD films. The inventors have now discovered that the relative compactness of these silicon oxide films is responsible for this difference.
The inventors achieved the instant invention as the result of extensive research into a method that would be capable of forming an organic solvent-insoluble, pinhole- and crack-free silicon oxide thick film wherein this film would be able to planarize height differences.gtoreq.1 micrometer by melting when heated and would not contain the silanol and alkoxy groups that are the cause of moisture absorption and carbon poisoning of the silicon oxide film product.